Pressure indicator



Sept. 16, 1941. F L, PRESCGT; 2,255,3GQ

PRESSURE INDICATOR Original Filed Feb. 9, 1934 2 Sheets-Sheet l [500RAM.

f o/Q0 L. Pegs 607-7- fI m/z W Sept. 16, 1941. F. L. PRESCOTT 2,255,80

PRESSURE INDICATOR Original Filed Feb. 9, 1934- 2 SheetsSheet 2 PatentedSept. 16, 1941 PRESSURETNDICATOR Ford L. Prescott, Dayton, Ohio Originalapplication February 9, 1934, Serial No. 710,500. Divided and thisapplication February 2, 1937, Serial No. 123,633

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) 6 Claims.

The invention described herein may be manufactured and used by or forthe Government for overnmental purposes, without the payment to me ofany royalty thereon.

The present invention relates to improvements in pressure indicators andmore particularly to indicators for recording the pressure diagrams ofhigh speed engines, particularly oi. the internal combustion type, andis a division of my copending application Serial No. 710,500, filedFebruary 9, 1934 which matured into Patent number 2,084,356, June 22,1937.

The prior art teaches the use of indicating instrumentalities fortesting and recording the pressure phenomena in high speed engines whichembrace the sampling, or point by point method whereby the completediagram of the average engine cycle is recorded.

In general, instruments of this character embody a sampler valve that isinterposed between the combustion space and an ordinary low speedindicator and a phase gear that is employed to drive the sampler valveat engine cam shaft speed; the phase gear being so constructed that thephase or point in the cycle at which the valve opens for a brief instantis adjustable manually. The drum of the low speed indicator is alsodriven by the phase gear so that as the period of opening of the samplervalve is moved through the cycle, the drum will be simultaneouslyactuated in an amount proportionate to the corresponding crank angle orpiston position. Continuous records are thus made oi. points taken froma large number of cycles of the engine. Suitable mechanism is providedbetween the phase gear and the recording drum so that the extent ofdisplacement of the indicator drum will correspond either to the pistondisplacement or to the crank angle, as the function of either of whichthe pressure phenomena may be re corded. 1

The sampler valves that have heretofore been employed in devices of thischaracter were remotely positioned from the point oi combustion and theyrequired a tube to connect the combustion space therewith; consequentlyintroducing in the card record a time lag the extent of which dependedupon the length of the tube connection and upon the rate at which thepressure is transmitted. Thus the entire card is caused to shift laterby that time lag.

A further phase error was introduced in th card due to considerablebacklashinthe gear train of the 'phase changing mechanism heretoforeemployed.

' The error'introduced in the card by prior devices in which a valve wasremotely positioned in the combustion chamber has been eliminated inaccordance with my invention by' positioning the sampler valvesubstantially at a wall of the combustion chamber.

The error that was introduced in the card by reason of the back lashpresent in the phase changing gear train of prior devices has beenpractically eliminated in accordance with my invention by reducing thenumber of gears to a minimum.

It has also been found by experiment that the sampler valves as well asthe pressure recording of the working surfaces under all operativeconditions.

Certain other and further objects of my invention will appear from thefollowing description of my invention taken in connection with theseveral view of the drawings.

Fig. 1 is a diagrammatic view of the system in which the several unitsare interconnected to produce a pressure time card and in which certainof the parts are shown in section.

Fig. 2 is a partial schematic view in side eleva tion and sectionshowing the particular arrangement of the sampler valve and itsinter-connections with the pressure recording element.

Fig. 3 is atransverse sectional view of the sampler valve taken on theline 3-3 of Fig. 2.

F18. 4 is a transverse sectional view taken on the line 4-4 of Fig. 3.

Fig. 5 is a sectional view taken on the line 55 of Fig. 3 and showingalso a fractional view of the driving connection.

Fig. 6 is a fractional side elevational view of the sampler unit. 0

Fig. 7 is an enlarged detail view of the poppet valve construction ofthe sampler valve shown in Fig. 3.

Fig. 8 is an enlarged detail view showing a modified form of the poppetvalve, and

Fig. 9 shows a pressure time card taken with the system of Fig. 1.

As illustrated herein and in accordance with my invention the systemshown in Fig. 1 for obtaining a pressure time card comprises essentiallya phase changing unit I that is driven by the engine crank-shaft I2 andoperatively connected to the sampler'valve unit I4 so that the samplerunit will admit gastherein under pressure during a. brief interval oncefor each cycle of operation of the engine. This phase changing unit isalso operatively connected to the recording drum I5 of the pressurerecording unit I6 so that with every change of position of the period ofadmittance of the valve relative to the cycle of operation, therecording drum will be moved to a position corresponding to said periodof admittance in said cycle.

The sampler unit it, as best shown in Figs. 2 to 6, consists of ahousing 552 that is provided with a cover plate Md and with a threadedstem portion I I6, which is adapted to be received withing a suitableopening within the combustion chamber, as shown in Fig. 1. The coverplate is formed with an annular pilot H8, that is received within acomplementary opening formed in the housing and is attached to thehousing by means of bolts I20 and nipples I22 for a purpose hereinafterdescribed.-

The complementary opening in the housing is made suficiently large topermit freedom of movement of the working parts disposed therein. A camI24 is journaled within the housing by means of bearings I26 and I28,that are respectively seated within openings I30 and I32, formed withinthe housing and cover plate.

ing shaft I36 that is universally connected with the phase gear throughthe universal connections I38 and I40 and the shaft I42, shown in Figs.1 and 5. A rocker I44 is disposed within the opening of the housing andpivotally mounted on a rocker shaft I46 that is press-fitted into anopening I48 formed in the housing at one end and received in an openingformed in the cover plate at the other end. The rocker is disposed Thecam has concentric broached opening I34 to receive a drivso that one armI50 is adapted to cooperate with the cam I24, whereas the other arm I52is seated on or cooperates with a poppet valve I54 of the sampler valve.The cam I24 is provided witha sharp lobe I56 so as to engage with thearm of the rocker to open the poppet valve for a brief interval. Thepoppet valve is slidably fitted with intervals when the valve is openthrough the outlet I19 and passageway I80 formed in the housing. Thediameter of the valve stem and the inner diameter of the valve seatopening or inlet IBI are made equal so that the pressure within thespace between the reduced portion and the wall of the bore I58 will holdthe poppet valve when in the closed position substantially balanced withrespect to the pressure on the outlet side thereof. Thus trappedrecording pressures will not tend to open the valve when the pressure inthe combustion chamber is less than the trapped recording pressures. Thehousing stem is formed with a counterbore I82 concentric with the boreI58 and is of a diameter equal to the diameter of the packing gland soas to provide a space between the poppet valve stem and the wall of thecounterbore to receive packings I84 and I86, that are held in spacedrelation by a' packing spacer I88. The packing spacer is provided withan annular groove I90 for communicating with a passageway E92 formed inthe housing and with perforations I9t for communicating oil to thepoppet valve stem.

A liquid seal is maintained between the working surfaces of the poppetvalve between the packings lad and I86 at a pressure that is in excessof the pressure of the gases that are trapped in the sampler valve by apredetermined amount that is constant regardless of the change inpressure of the trapped gas. This is accomplished by providing a chamberI96 that is partially filled with sealing liquid I98, preferably oil,the chamber being so disposed with respect to the poppet valve that thesealing liquid within the chamber is above the passageway I92, tomaintain at all times a pressure supply of sealing liquid to the packingspacer corresponding to the static head pressure of the liquid in thechamber and the pressure of the trapped gas. Communication between thebottom of the chamber and the passageway of the housing is establishedby means of pipe connections 200. The air space 202 above the sealingliquid in the chamber is in communication with the passageway I80 of thesampler valve by means of pipe connections 204. In this manner gasesthat are trapped within the sampler valve together with the static headpresthe stem of the housing and within an opening I60 formed in thegland I62. The poppet valve is formed with a head I64 which ispositioned approximately at the wall of the combustion chamber of theengine cylinder 20 and is seated against the valve seat I66 formed onthe housing stem H6, as shown in Figs. 3 and 6, and is held in seatedrelation by means of a compression spring I68; that is disposed betweena gland locking retainer I10 and a lock nut I12 that is threaded ontothe valve stem. interposed between the rocker arm I52 and the lock nutI12 is a tappet nut I14 that is threaded onto the poppet valve stem. Thegland locking member I10 is formed with an opening at one end that slipsover the gland and is attached to the housing by a screw I18 for fixingthe gland in position.

As shown in Figure 7. the poppet valve at its lowerend and adjacent thehead I64 is Iormed,

with a. reduced portion I18 to permit the gases sure of the liquid inthe chamber I96 will exert their premure influence against the sealingliquid, which by reason of its communication with the packing spacerwill maintain within the spacer a pressure of sealing liquid at alltimes greater than the pressure of the entrapped gases at the bottom ofthe packing on outlet side of the valve, thus preventing leakage of thegases.

Any suitable low speed pressure indicator may be employed as a recordingmeans for obtaining prwsure volume or pressure time card, and, asillustrated herein, the Maihak type of pressure recording indicator isemployed for this purpose. The recording stylus 206, Fig. 1 of thisrecording pressure indicator is actuated by the pressure of theentrapped gasm in the sampler valve and is preferably actuated throughthe liquid seal medium so that the escape of the gases through theworking surfaces of the pressure recording de-- vice is prevented. Thisis accomplished by establishing communication between the bottom of toflow irom the combustion cham er d nl the device is provided with aconventional three-way on the card. From the foregoing description itwill be apparent thztt the intense pressures of the gaseous fluids inthe internal combustion engine. are not only transmitted to therecording device by means of a liquid medium, but that in additionthereto the said liquid medium serves to provide a liquid seal for theworking surfaces of both the sampler valve andthe pressure recordingdevice.

In order to prevent air leakage within the liquid seal system especiallywhen the engine is running under pressure below atmosphere, 8. reservoir220 of sealing liquid 222 may be connected to the atmospheric opening 2|8 ofthe indicator cock by means of a pipe connection 22I. In this wayshould the pressure within the sampler valve be less than atmosphere thepressure differential between the atmosphere and that of the samplervalve will force some of the oil within the reservoir 220 into thesystem instead of allowing air to leak in.

The pressure recording device has the conventional recording drum I5,which is actuated by an indicator cord 224. one nd of which is connectedto the drum I5, the other end of which is connected to an extension 226,1, formed on the member I02 that carries the scale I06 so that for anyadjustment of the phase changing gear the recorder drum will assume acorresponding position. It will therefore be obvious that the recordedpressure is correlated to the time in the cycle of the period of openingthe sampler valve, thus producing a pressure time record of the pressurecycle.

A suitable provision is made for dissipating the excess heat of thesampler valve. This is accomplished by circulating a cooling liquidthrough a suitable passageway 228i0rmed in the wall of the housing, thepassageway 230 constituting an inlet and the passageway 232 constitutingan outlet that are in communication with the passageway 228. The coolingliquid is supplied from a source of supply (not shown) and enters andleaves through the nipples I22, which nipples are preferably providedwith threaded stems that pass through openings formed in the cover plateand serve to fasten the cover plate to the housing of the sampler valve.

The modification of sampler valve shown in Fig. 8 is similar inconstruction and design to the sampler valve shown in Fig. '7, exceptthat the poppet valve is formed with a plurality of circumferential oilgrooves disposed in spaced relation along the length of the poppet valvestem having a close fit with a valve guide. The valve guide has apressed fit; with the opening formed in the housing stem H6 and isprovided with an annular recess 234 at the point which communicates withpassageway 236 and is provided with a plurality of orifices forcommunication with an annulus 238. The sealing liquid is fed to theannulus in the same manner as it was before to the packing spacer inFig. 7 to eifect the liquid seal. By this arrangement the necessity forreplacing the soft packing, as shown in Fig. 7, is eliminated,

In the operation the device is set at any identifying position inrelation to the cycle of operaations of the engine, as, for example, attop dead center of the engine piston. The phase gear is then adjusted bycrank wheel 98 so that the sampler valve open at that predeterminedposition of the engine piston. When obtaining a pressure time card, theadjustable scale carrying member I02 is moved so that the index III!will.

indicate a corresponding position on the scale. A card is placed aroundthe pressure recording drum and with the stylus pressed" against thepaper, the phase gear is slowly rotated by means of the crank wheel andhandle 9t throughout one revolution ofthe phase gear. At the same timeas the phase gear is being rotated the period of opening of the samplervalve is being moved through a corresponding engine crank angle.

Thus, as the sampler valve taps the cylinder pressure-for a briefinstant at gradually changing points in the cycle, the indicator stylusrecords automatically a series of pressure changes resulting ina'distinct, continuous line of pressure-time relations on the card. Themany small increments of pressure change in a given rotary movement ofthe recording drum makes possible an extremely accurate record, as noinertia eifect in the recording mechanism is involved.

In the case of pressure-time diagrams, top-center is determined bytaking a compression card and noting where, on card and phase geargraduations, the peak of pressure occurs. On subsequent cards, a touchof the finger on the stylus, when this point is reached, establishes itas a reference point on the paper.

In making these cards the phase gear is rotated in the direction inwhich it was rotated in determining the top center and preferably so asto pass through theengine cycle in natural order of events.

During each period of opening of the sampler valve, a minute quantity ofgas passes through the valve and equalizes the pressure within thesampler valve and recording cylinder 208 to that of the engine cylinderand the pressure of the gas within the sampler is trapped by thebalanced poppet valve and remains constant until the next period ofopening. The gas that is trapped within the sampler and itscommunication, to the sealing liquid chamber exerts its pressure uponthe liquid which transmits greater pressure to a point along the workingsurface of the poppet valve to provide a positive liquid seal againstgas leakage and also transmits its pressure to the recording styluspiston 2I4 to actuate the stylus in accordance with the instant pressureof the gas. The liquid transmitting medium serves also to prevent thecorrosive action of the gases upon the working surfaces which wouldotherwise take place if the sealing liquid were not employed.

What I claim is:

1. In a device for manifesting the pressure in an engine cylinder,pressure responsive indicating means, means defining a pressure passagebetween said cylinder and said pressure responsive means, valve meansfor admitting pressure from said cylinder to said passage, said lastmentioned means comprising a valve body having a valve seat, a normallyclosed valve member slidably mounted in said body at one end and seatingon said seat at the other end, means by which said valve may bemomentarily opened to admit pressure, and a liquid in said passage incommunication with the space between said valve member and said valvebody and subject, at all times, to an initial substantial pressure headand responsive to said admitted pressure to prevent escape of saidadmitted pressure past said one end, said liquid being furthercommunicatively connected with said pressure responsive indicating meansfor actuating the same.

2. In a device for indicating the pressure in an engine cylinder at adesired point in the ,jeng'me cycle comprising, a valve body having apassage therein terminating in a port communicating with said cylinder,a poppet valve seated in said port for controlling communication betweensaid cylinder and said passage, a valve stem for said valve reciprocablein a guide formed in said valve body, timed actuating means .tormomentarily lifting said valve off its seat, an annular channel in saidvalve guide, a lubricant supply source connected to said channel tolubricate said valve stem, a connection between said passage in saidvalve body" and said lubricant supply source to transmit the pressure insaid passage thereto to prevent leakage of the pressure medium along thevalve stem, and pressure responsive measuring means connected to saidlubricant supply source to indicate the pressure existing within saidpassage.

3. In a device for indicating the pressure in an engine cylinder,pressure responsive indicating means, a valve body having a. normallyclosed chamber therein, a port for connecting said means and saidlubricant supply source, whereby vthe pressure of the lubricant fromsaid supply source prevents pressure leakage from said chamber alongsaid valve and also serves as a measure of the value of the existingpressure in said chamber.

4. The structure as claimed in claim 3; in which the level of the sourceof lubricant supply is arranged so that an initial static head isexerted at the point of communication of said supply with the clearancespace between the valve and valve guide,

5. In a device for measuring the pressure at a desired point in thecycle in an engine cylinder, a valve body having a normally closedchamber therein, a passage connecting said chamber with the interior ofthe engine cylinder, a timed reciprocable valve for controlling flowbetween chamber to the engine cylinder, a reciprocable valve in saidvalve body for controlling fiuid flow through said port, a guide in saidvalve body for guiding said valve and providing a small clearance spacetherebetween, a source of lubricant supply, a flow connection betweensaid source and the clearance space between the valve and valve guide, apassage in said valve body for transmitting the gas pressure in saidchamber to said lubricant supply source and a connection between saidpressure responsive indicating said cylinder and said chamber throughsaid passage to trap gas samples in said chamber, a valve guide in saidvalve bodyfor reciprocably guiding said valve and providing a smallworking clearance therebetween, a source of lubricant supply, a flowconnection between said supply and the clearance space between saidvalve guide and said valve, and a pressure transmitting connectionbetween said lubricant supply and said chamber, whereby said supply issubjected to the pressure existing within said chamber.

6. The structure as claimed in claim 5, in which the level of the sourceof lubricant supply is arranged so that an initial static head isexerted at the point of communication of said supply with the clearancespace between the valve and valve guide.

FORD L. PRESCOTT.

